Barrier polishing fluid

ABSTRACT

The polishing fluid is useful for polishing tantalum-containing barrier materials of a semiconductor substrate. The polishing fluid includes a nitrogen-containing compound having at least two nitrogen atoms comprising imine compounds and hydrazine compounds. The nitrogen-containing compound is free of electron-withdrawing substituents; and the polishing fluid is capable of removing the tantalum-containing barrier materials from a surface of the semiconductor substrate without an abrasive.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of U.S. application Ser. No. 10/670,587filed Sep. 25, 2003, now U.S. Pat No. 7,241,725.

BACKGROUND

The invention relates to polishing semiconductor substrates and, moreparticularly, to an abrasive-free polishing fluids to remove barrierlayers.

Circuit interconnects for semiconductor devices can be formed in adielectric layer in which multiple trenches are arranged. Theinterconnects are formed by applying a barrier film over the underlyingdielectric layer, followed by applying a metal layer over the barrierfilm. The metal layer is formed to a sufficient thickness to fill thetrenches with metal. The interconnect fabrication process includes theuse of a two-step chemical mechanical polishing (CMP) process.

CMP refers to a process of polishing a semiconductor wafer with apolishing pad and a polishing fluid. In a first polishing step, themetal layer is removed from the underlying barrier film and from theunderlying dielectric layer. The metal layer is removed, both byabrasion applied by the polishing pad, and by chemical reaction with thepolishing fluid accompanied by dissolution of the products of chemicalreaction. The first polishing step removes the metal layer, leaving asmooth planar polished surface on the wafer, and further leaving metalin the trenches to provide circuit interconnects that are substantiallyplanar with the polished surface. In addition to metal removal, somefirst-step polishing processes require removal of a dielectric layer.For example, Lee et al., in EP Pat. Pub. No. 1 072 662 A1, disclose theuse of guanidine as an abrasion accelerator for accelerating an abrasivecomposition's dielectric removal rate.

A typical first-step polishing process includes an aqueous solutionhaving an oxidizing reagent, such as KNO₃ or H₂O₂, in a polishing fluidto remove copper interconnects. The copper metal layer is removed byoxidation of the metal layer by the oxidizing reagent, and by abrasionof the polishing pad. Further, the polishing pad abrades the metal layerto minimize redeposition of the dissolved oxides from the solution ontothe surface of the material being polished. The copper is removed froman underlying barrier film, for example, of tantalum (Ta) or tantalumnitride (TaN). The barrier film is more resistant to abrasion than isthe copper, such that the barrier film acts as a polish stop forstopping the first-step polishing of copper. Further, oxidation of thesurface of the barrier film by the polishing fluid will inhibit itsremoval during first-step polishing.

In a second polishing step, the barrier film is removed from theunderlying dielectric layer. Second-step polishing can provide a smooth,planar polished surface on the dielectric layer. Ideally, the secondpolishing step does not remove excessive metal in the trenches. Excessmetal removal in the second polishing step can contribute to dishing.

Dishing is a term of art that describes the formation of unwantedcavities in the circuit interconnects caused by removing excess metal inthe trenches. Dishing can occur in both the first polishing step and inthe second polishing step. The circuit interconnects are required tohave precise dimensions that determine the electrical impedance ofsignal transmission lines, as provided by the circuit interconnects.Dishing in excess of acceptable levels causes dimensional defects in thecircuit interconnects, which can contribute to attenuation of electricalsignals transmitted by the circuit interconnects.

The second polishing step should cause minimal erosion. Erosion is aterm of art that describes the unwanted lowering of the surface of thedielectric layer caused by removing some of the dielectric layerunderlying the barrier film. Erosion that occurs adjacent to the metalin the trenches causes dimensional defects in the circuit interconnects,which can contribute to attenuation of electrical signals transmitted bythe circuit interconnects. To minimize erosion, a polishing fluid forsecond-step polishing is desired to remove the barrier film with ahigher removal rate than the removal rate for the dielectric layer.

The second polishing step should have high removal selectivity for thebarrier layer relative to the underlying layers. Removal selectivity isdefined as a ratio of the removal rate of the barrier film, relative tothe removal rate of the comparison layer, for example a dielectric layeror a metal film. For purposes of this specification, selectivity refersto the ratio in removal rate in distance per unit time, such asangstroms per minute. Thus, removal selectivity is a measure of theremoval of the barrier film relative to the dielectric layer or themetal film. In addition, increased removal selectivities can improvepolishing performance. Polishing with a polishing fluid that exhibits ahigh removal selectivity relative to the dielectric layer increasesremoval of the barrier film and decreases removal of the dielectriclayer.

State of the art slurries require significant quantities of abrasiveparticles to remove barrier layers. Unfortunately, these slurries oftenresult in unacceptable dishing of metal interconnects and dielectricerosion. In view of this, there is an ongoing desire for a barrierremoval composition that removes barriers at a high rate with reduceddishing of metal interconnects and erosion of dielectrics.

STATEMENT OF INVENTION

The invention provides a polishing fluid useful for polishingtantalum-containing barrier materials of a semiconductor substratecomprising: a nitrogen-containing compound having at least two nitrogenatoms comprising at least one of a compound of a formula selected fromthe group comprising:

wherein R¹ comprises —H or —NH₂ and R², R³, R⁴, R⁵ and R⁶ independentlycomprise substituents selected from the group consisting of —H, ahydrocarbon group, an amino group, a carbonyl group, an imido group, anazo group, a cyano group, a thio group, a seleno group and —OR⁷ where R⁷comprises a hydrocarbon group, and the nitrogen-containing compoundbeing free of electron-withdrawing substituents; and the polishing fluidbeing capable of removing the tantalum-containing barrier materials froma surface of the semiconductor substrate without an abrasive.

An additional aspect of the invention provides a polishing fluid usefulfor polishing tantalum-containing barrier materials of a semiconductorsubstrate comprising: 0 to 6 inhibitor for reducing the removal of aninterconnect metal; 0 to 1 weight percent abrasive particles; 0 to 25oxidizing agent; 0 to 15 complexing agent and 0.05 to 25nitrogen-containing compound having at least two nitrogen atomscomprising at least one of a compound of a formula selected from thegroup comprising:

wherein R¹ comprises —H or —NH₂ and R², R³, R⁴, R⁵ and R⁶ independentlycomprise substituents selected from the group consisting of —H, ahydrocarbon group, an amino group, a carbonyl group, an imido group, anazo group, a cyano group, a thio group, a seleno group and —OR⁷ where R⁷comprises a hydrocarbon group, and the nitrogen-containing compoundhaving an electron-donating substituent; and the polishing fluid beingcapable of removing the tantalum-containing barrier materials from asurface of the semiconductor substrate without an abrasive.

In addition, the invention provides a method for polishing asemiconductor substrate, the semiconductor substrate having a metalinterconnect layer and a tantalum-containing barrier layer adjacent themetal interconnect layer comprising: polishing a barrier layer apolishing fluid to remove at least a portion of the tantalum-containingbarrier layer, the polishing fluid being abrasive-free and comprising anitrogen-containing compound having at least two nitrogen atomscomprising at least one of a compound of a formula selected from thegroup comprising:

wherein R¹ comprises —H or —NH₂; and R², R³, R⁴, R⁵ and R⁶ independentlycomprise substituents selected from the group consisting of —H, ahydrocarbon group, an amino group, a carbonyl group, an imido group, anazo group, a cyano group, a thio group, a seleno group and —OR⁷ where R⁷comprises a hydrocarbon group, and the nitrogen-containing compund beingfree of electron-withdrawing substituents.

DETAILED DESCRIPTION

In a preferred embodiment of the invention, an abrasive-free polishingfluid is formulated with a nitrogen-containing polishing agent such asan imine derivative compound or a hydrazine derivative compound.

Preferred imine derivatives include compounds of formula (I):

where R¹ is —H or —NH₂ and R² is —H, —NH₂, a hydrocarbon group, an aminogroup, a carbonyl group, an imido group, an azo group, a cyano group, athio group, or a seleno group and —OR⁷ where R⁷ is a hydrocarbon group.

Preferred hydrazine derivatives include compounds of formula (II):R³R⁴N—N R⁵R⁶  (II)and where R³, R⁴, R⁵, and R⁶ are independently —H, —OR⁷, —NH₂, ahydrocarbon group, a carbonyl group, an imido group, an azo group, acyano group, a thio group, or a seleno group.

The term “nitrogen-containing” refers to a substance containing two ormore nitrogen atoms. Two or more nitrogen atoms in a nitrogen-containingsubstance may be bonded to each other, or they may be separated by otheratoms. If a nitrogen-containing substance contains three or morenitrogen atoms, some of the nitrogen atoms may be bonded to each otherwhile others may be bonded to non-nitrogen atoms only. A nitrogen atomin a nitrogen-containing substance may be part of a chemical groupwithin the substance, such as an amino, amido, azo, imino, imido, orhydrazino group. Preferably, the nitrogen atoms in a nitrogen-containingsubstance are in their reduced state and are not bonded directly to anoxygen atom (i.e. —NO₂; —NO₃).

The term “hydrocarbon group” refers to a straight, branched or cyclicchain of carbon atoms substituted with hydrogen atoms, and includesunsubstituted and substituted alkyl groups, alkenyl groups, alkynylgroups, aryl groups, and heterocyclyl groups. Preferably, a hydrocarbongroup contains from 1 to 20 carbon atoms. A hydrocarbon group mayoptionally be substituted with other groups. The bonds between thecarbon atoms may be independently selected from single bonds, doublebonds, and triple bonds.

The term “alkyl” (or alkyl- or alk-) refers to a substituted orunsubstituted, straight, branched or cyclic hydrocarbon chain thatpreferably contains from 1 to 20 carbon atoms. Alkyl groups include, forexample, methyl, ethyl, propyl, isopropyl, cyclopropyl, butyl,iso-butyl, tert-butyl, sec-butyl, cyclobutyl, pentyl, cyclopentyl, hexyland cyclohexyl.

The term “alkenyl” (or alkenyl- or alken-) refers to a substituted orunsubstituted, straight, branched or cyclic hydrocarbon chain thatcontains at least one carbon-carbon double bond, and that preferablycontains from 2 to 20 carbon atoms. Alkenyl groups include, for example,ethenyl (or vinyl, —CH═CH₂); 1-propenyl; 2-propenyl (or allyl,—CH₂—CH═CH₂); 1,3-butadienyl (—CH═CHCH═CH₂); 1-butenyl (—CH═CHCH₂CH₃);hexenyl; pentenyl; 1,3,5-hexatrienyl; cyclohexadienyl; cyclohexenyl;cyclopentenyl; cyclooctenyl; cycloheptadienyl; and cyclooctatrienyl.

The term “alkynyl” (or alkynyl- or alkyn-) refers to a substituted orunsubstituted, straight, branched or cyclic hydrocarbon chain thatcontains at least one carbon-carbon triple bond, and that preferablycontains from 2 to 20 carbon atoms. Alkynyl groups include, for example,ethynyl (or acetylenyl, —C≡CH₂); 2-methyl-3-butynyl; and hexynyl.

The term “aryl” refers to any substituted or unsubstituted aromaticcarbocyclic group that preferably contains from 3 to 20 carbon atoms. Anaryl group can be monocyclic or polycyclic. Aryl groups include, forexample, phenyl, naphthyl, biphenyl, benzyl, tolyl, xylyl, phenylethyl,benzoate, alkylbenzoate, aniline, and N-alkylanilino.

The term “heterocyclyl group” refers to a saturated, unsaturated, oraromatic ring moiety that contains one or more heteroatoms, and thatpreferably contains from 5 to 10, more preferably from 5 to 6, ringatoms. The term “ring atoms” refers to atoms that are incorporated intothe ring structure and excludes other atoms that are pendant to thering. The ring can be mono-, bi- or polycyclic. A heterocyclic groupcontains carbon atoms and from 1 to 3 heteroatoms independently selectedfrom the group consisting of nitrogen, oxygen, and sulfur. Heterocyclicgroups, which may also be substituted or unsubstituted, include, forexample, benzimidazole, benzotriazole, furan, imidazole, indole,isoquinoline, isothiazole, morpholine, piperazine, pyrazine, pyrazole,pyridine, pyrimidine, pyrrole, quinoline, thiazole, thiophene, triazinesand triazole.

The term “substituted,” when used to describe a chemical group, refersto a chemical moiety that contains at least one, preferably from 1 to 5substituents. Suitable substituents include, for example, hydroxyl(—OH), amino (—NH₂), oxy (—O—), carbonyl (>C═O), thiol, alkyl, halo,nitro, aryl and heterocyclic groups. These substituents can optionallybe further substituted with from 1 to 5 substituents.

The term “amino group” refers to a group bonded to a substance through anitrogen atom. For example, an amino group may be selected from thegroup comprising —NH₂; alkylamino (—NH-alkyl); dialkylamino(—N-(alkyl)₂); arylamino (—NH-aryl); and substituted derivativesthereof. Preferably, the alkyl groups bonded to the nitrogen containfrom 1 to 20 carbon atoms, and the aryl groups bonded to the nitrogencontain from 3 to 20 carbon atoms. The alkyl groups in a dialkylaminogroup may be the same or may be different.

The term “carbonyl group” refers to a group containing a carbon atomdoubly bonded to an oxygen atom, and includes carboxylic acids,anhydrides, carbonates, aldehydes, ketones, esters, carboxylic acidhalides, and amides. For example, a carbonyl group may have the generalformula (III):

where R⁸ is —H, —OH, —OR⁹, —R¹⁰, —NH₂, and —NH—C(═O)—R¹¹; and R⁹, R¹⁰,and R¹¹ are independently alkyl groups containing from 1 to 10 carbonatoms.

The term “imido group” refers to a group containing a carbon atom doublybonded to an —NH group. For example, an imido group may have the generalformula (IV):

where R¹² is —H, —NH₂, or an alkyl group containing from 1 to 10 carbonatoms. The term “azo group” refers to a group containing anitrogen-nitrogen double bond, or an —NH group singly bonded to another—NH group. For example, an azo group may be selected from the groupconsisting of —N₃; —NH—NH—NH₃; —N═N—NH₃; —N═N—R¹³; —R¹⁴═N—N═R¹⁵; and—NH—NH—R¹⁶; where R¹³, R¹⁴, R¹⁵, and R¹⁶ are independently alkyl groupscontaining from 1 to 10 carbon atoms.

The term “cyano group” refers to a group containing a triple bondbetween a carbon atom and a nitrogen atom, or a carbon atom doublybonded to a nitrogen atom and also doubly bonded to another heteroatomsuch as oxygen, sulfur, or selenium. For example, a cyano group may beselected from the group consisting of —C≡N; —N≡C; —N═C═O; —N═C═S; and—N═C═Se.

The term “thio group” refers to a group containing a sulfur atom singlybonded to another atom. For example, a thio group may be selected fromthe group consisting of —S—R¹⁷; —S—S—R¹⁸; —S—C≡N; —SO₂H; and —SOH; whereR¹⁷ and R¹⁸ are independently alkyl groups containing from 1 to 10carbon atoms.

The term “seleno group” refers to a group containing a selenium atomsingly bonded to another atom. For example, a seleno group may beselected from the group consisting of —Se—R¹⁹; —Se—Se—R²⁰; and —Se—C≡N;where R¹⁹ and R²⁰ are independently alkyl groups containing from 1 to 10carbon atoms.

Preferred imine derivatives of formula (I) include, for example,1,3-diphenyl guanidine, guanidine hydrochloride, tetramethylguanidine,formamidine acetate, and acetamidine hydrochloride.

Preferred hydrazine derivatives of formula (II) include, for example,carbohydrazide, imidazole, acetic hydrazide, semicarbazidehydrochloride, and formic hydrazide.

Imine derivative compounds of formula (I) preferably contain anelectron-donating substituent as R¹ or R², and are free ofelectron-withdrawing substituents. More preferably, one of R¹ and R² isan electron-donating substituent, and the other substituent is eitherhydrogen or an electron-donating substituent. If two electron-donatingsubstituents are present in an imine derivative compound, thesubstituents may be the same, or they may be different.

Imine derivative compounds of formula (II) preferably contain ahydrazine functionality (>N—NH₂) and contain no more than oneelectron-withdrawing substituent. A hydrazine functionality is providedwhen R³ and R⁴ are both hydrogen, or when R⁵ and R⁶ are both hydrogen.

For purposes of the specification, the term “electron-donating” refersto a chemical group bonded to a substance that transfers electrondensity to that substance. F. A. Carey and R. J. Sundberg, in AdvancedOrganic Chemistry, Part A: Structure and Mechanisms, 3^(rd) Edition NewYork: Plenum Press (1990), p. 208 and 546-561 provide a more detaileddescription of electron-donating substituents. The imine derivativecompounds have an electron-donating substituent that transferssufficient electron density to the substance to establish a measurablepartial positive charge on the substituent. Electron-donatingsubstituents include, for example, amino, hydroxyl (—OH), alkyl,substituted alkyl, hydrocabon radical, substituted hydrocarbon radical,amido, and aryl. These electron-donating substituents accelerate removalof tantalum-containing barrier materials.

In addition, abrasive additions render imine and hydrazine derivativecompounds effective with electron-withdrawing substituents. The term“electron-withdrawing” refers to a chemical group bonded to a substancethat transfers electron density away from that substance.Electron-withdrawing substituents transfer sufficient electron densityaway from the substance to establish a measurable partial negativecharge on the substituent and do not accelerate barrier removal.Electron-withdrawing substituents include, for example, —O-alkyl;-halogen; —C(═O)H; —C(═)O-alkyl; —C(═O)OH; —C(═O)-alkyl; —SO₂H; —SO₃H;and —NO₂. The carbonyl groups that are electron-withdrawing are notamide groups.

The nitrogen-containing polishing agent may be present in the fluid in arange of concentrations, for example from 0.05 to 25 weight percent.This specification refers to compositions by weight percent, unlessspecifically expressed otherwise. A single type of nitrogen-containingpolishing agent may be present, or mixtures of nitrogen-containingpolishing agents may be used. Preferably, the concentration ofnitrogen-containing polishing agent is from 0.1 to 10 weight percent.More preferably, the concentration of nitrogen-containing polishingagent is from 1 to 5 weight percent. Even more preferably, theconcentration of nitrogen-containing polishing agent is from 1.5 to 3weight percent. In a most preferred embodiment, the concentration ofnitrogen-containing polishing agent is at least 2 weight percent.

Optionally, the composition contains 0 to 25 weight percent oxidizer.Preferably, the composition contains 0 to 15 weight percent oxidizer.The oxidizer is particularly effective in accelerating the removal rateof interconnect metals, such as copper. The oxidizing agent can be atleast one of a number of oxidizing compounds, such as hydrogen peroxide(H₂O₂), monopersulfates, iodates, magnesium perphthalate, peraceticacid, periodates, perbromates, perchlorates, persulfates, bromates,nitrates, iron salts, cerium salts, Mn (III), Mn (IV) and Mn (VI) salts,silver salts, Cu salts, chromium salts, cobalt salts, halogenshypochlorites and mixtures thereof. Furthermore, it is oftenadvantageous to use a mixture of oxidizer compounds. The mostadvantageous oxidizers are hydrogen peroxide and iodate. When thepolishing fluid contains an unstable oxidizing agent, such as hydrogenperoxide, it is often most advantageous to mix the oxidizer into theslurry at the point of use. Since this composition operates without anoxidizer at pH level above 7, most advantageously, the compositioncontains no oxidizer to limit undesirable static etch of metalinterconnects, such as, copper. At pH levels below 7, the fluid requiresan oxidizer to facilitate barrier removal.

The barrier removal agent provides efficacy over a broad pH range insolutions containing a balance of water. This solution's useful pH rangeextends at least from 2 to 12. Preferably, the solution has a pH between7 and 12. Most preferably, the solution's pH is between 8 and 11.Typical agents for adjusting pH downward include nitric acid, sulfuricacid, hydrochloric acid, phosphoric acid and organic acids. Mostpreferably, potassium hydroxide and nitric acid provide final pHadjustments. In addition, the solution most advantageously relies upon abalance of deionized water to limit incidental impurities.

The polishing fluid for selective removal of a barrier layer contains anitrogen-containing polishing agent in an aqueous mixture. The polishingfluid may also optionally contain a metal corrosion a complexing agent,a biocide, and a salt (for example a chloride salt such as ammoniumchloride), as well as other additives that do not interfere with the CMPprocess.

Suitable metals used for the interconnect include, for example, copper,copper alloys, gold, gold alloys, nickel, nickel alloys, platinum groupmetals, platinum group metal alloys, silver, silver alloys, tungsten,tungsten alloys and mixtures comprising at least one of the foregoingmetals. The preferred interconnect metal is copper. In acidic polishingcompositions and fluids that utilize oxidizers such as hydrogenperoxide, both the copper removal rate and the static etch rate are highprimarily because of oxidation of the copper. In order to reduce theremoval rate of the interconnect metal the polishing composition employsa corrosion inhibitor. The corrosion inhibitor's function is to reduceremoval of the interconnect metal. This facilitates improved polishingperformance by reducing the dishing of the interconnect metal.

The inhibitor is typically present in an amount 0 to 6 weightpercent--the inhibitor may represent a single or a mixture of inhibitorsto the interconnect metal. Within this range, it is desirable to have anamount of inhibitor greater than or equal to 0.0025 weight percent,preferably greater than or equal to 0.10 weight percent. Also desirablewithin this range is an amount of less than or equal to 4 weightpercent, preferably less than or equal to 1 weight percent. Thepreferred corrosion inhibitor is benzotriazole (BTA). In one embodiment,the polishing composition may contain a relatively large quantity of BTAinhibitor for reducing the interconnect removal rate. At BTAconcentrations above 0.25 weight percent, an addition of supplementalcorrosion inhibitors may be unnecessary. The preferred concentration ofBTA is an amount of 0.0025 to 2 weight percent.

Exemplary complexing agents for optional use in the polishing fluidinclude acetic acid, citric acid, ethyl acetoacetate, glycolic acid,lactic acid, malic acid, oxalic acid, salicylic acid, sodium diethyldithiocarbamate, succinic acid, tartaric acid, thioglycolic acid,glycine, alanine, aspartic acid, ethylene diamine, trimethylene diamine,malonic acid, gluteric acid, 3-hydroxybutyric acid, propionic acid,phthalic acid, isophthalic acid, 3-hydroxy salicylic acid, 3,5-dihydroxysalicylic acid, gallic acid, gluconic acid, pyrocatechol, pyrogallol,gallic acid, tannic acid and salts thereof. Preferably, the complexingagent used in the polishing fluid is citric acid. Most advantageously,the polishing fluid contains 0 to 15 weight percent complexing agent.

Although the nitrogen-containing polishing agents provide efficaciousabrasive-free polishing fluids, it may be desirable to add an abrasiveto the polishing fluid in some applications. The polishing compositionmay optionally contain up to 25 wt % abrasive to facilitate silicaremoval or combined barrier and silica removal—depending upon theintegration scheme, the polishing composition may serve to remove themask layer or to first remove a barrier layer and then remove a siliconoxide-containing layer. The polishing composition optionally includes anabrasive for “mechanical” removal of barrier layers. The abrasive ispreferably a colloidal or fumed abrasive. Example abrasives includeinorganic oxides, metal borides, metal carbides, metal nitrides, polymerparticles and mixtures comprising at least one of the foregoing.Suitable inorganic oxides include, for example, silica (SiO₂), alumina(Al₂O₃), zirconia (ZrO₂), ceria (CeO₂), manganese oxide (MnO₂), orcombinations comprising at least one of the foregoing oxides. Modifiedforms of these inorganic oxides such as polymer-coated inorganic oxideparticles and inorganic coated particles may also be utilized ifdesired. Suitable metal carbides, boride and nitrides include, forexample, silicon carbide, silicon nitride, silicon carbonitride (SiCN),boron carbide, tungsten carbide, zirconium carbide, aluminum boride,tantalum carbide, titanium carbide, or combinations comprising at leastone of the foregoing metal carbides, boride and nitrides. Diamond mayalso be utilized as an abrasive if desired. Alternative abrasives alsoinclude polymeric particles and coated polymeric particles. Thepreferred abrasive is silica.

To limit erosion and dishing, it is advantageous to use the abrasive inan amount of less than 5 weight percent. Using 0 to 1 or less than 1weight percent abrasive further facilitates limiting dishing anderosion. Most advantageously, the polishing fluid contains no abrasiveto further reduce dishing and erosion.

The abrasive has an average particle size of less than or equal to 150nanometers (nm) for preventing excessive metal dishing and dielectricerosion. For purposes of this specification, particle size refers to theaverage particle size of the abrasive. It is desirable to use acolloidal abrasive having an average particle size of less than or equalto 100 nm, preferably less than or equal to 50 nm, and more preferablyless than or equal to 40 nm. The least dielectric erosion and metaldishing advantageously occurs with colloidal silica having an averageparticle size of less than or equal to 40 nm. Decreasing the size of thecolloidal abrasive to less than or equal to 40 nm, tends to improve theselectivity of the polishing composition; but it also tends to decreasethe barrier removal rate. In addition, the preferred colloidal abrasivemay include additives, such as dispersants, surfactants and buffers toimprove the stability of the colloidal abrasive at acidic pH ranges. Onesuch colloidal abrasive is colloidal silica from Clariant S. A., ofPuteaux, France. The chemical mechanical planarizing composition canalso optionally include brighteners, such as, ammonium chloride,complexing agents, chelating agents, pH buffers, biocides and defoamingagents.

If the polishing composition does not contain abrasives, then padselection and conditioning become more important to the chemicalmechanical planarizing (CMP) process. For example, for someabrasive-free compositions, a fixed abrasive pad improves polishingperformance.

The solution relies upon a barrier removal agent to removetantalum-containing barrier materials. For purposes of thisspecification, tantalum-containing barrier materials refer to tantalum,tantalum-containing alloys, tantalum-base alloys and tantalumintermetallics. The solution has particular effectiveness for tantalum,tantalum-base alloys and tantalum intermetallics, such as tantalumcarbides, nitrides and oxides. The slurry is most effective for removingtantalum and tantalum nitride barriers from patterned semiconductorwafers.

Typical dielectric materials used in composite semiconductor substratesinclude SiO₂, tetraethylorthosilicate (TEOS), phosphosilicate glass(PSG), boron phosphosilicate glass (BPSG), or a low-k dielectric. Low-kdielectrics include porous silica and organic low-k dielectrics, such asfluoropolymers and copolymers.

It is desirable not to remove the metal at a high rate to avoid dishing.It is also desirable not to remove the dielectric at a high rate toavoid erosion. Preferably, the removal selectivity of the polishingfluid for the barrier relative to the dielectric is at least 10, andmore preferably at least 20, and even more preferably at least 50, andstill more preferably at least 100. Preferably, the removal selectivityof the polishing fluid for the barrier relative to the metal is at least5, and more preferably at least 10, and most preferably at least 15.

EXAMPLES

Experiments were conducted to test variations in the composition of apolishing fluid for second-step polishing by CMP to remove, atreasonable rates, a barrier film of TaN from an underlying dielectriclayer of silica on a semiconductor wafer, while minimizing erosion ofthe dielectric layer and minimizing dishing of metal in the trenches ona semiconductor wafer. Removal rates were determined on (200 mm)semiconductor wafers polished with the recited polishing fluids on aStrausbaugh polishing machine using a Politex polishing pad (availablefrom Rodel, Inc., Newark, Del.) under downforce conditions of about 3pounds per square inch (psi) or 20.7 kPa and a polishing fluid flow rateof about 200 cubic centimeters per minute (cc/min). Experiments wereperformed by separately polishing a barrier film of tantalum nitride(TaN), a dielectric layer of tetraethylorthosilicate (TEOS) and a metalfilm of copper (Cu), using a polishing pad and a polishing fluid.

The polishing fluids tested were at pH 9 (pH adjusted with potassiumhydroxide, nitric acid and balance deionized water) and contained 0.1wt. % benzotriazole (BTA) and 0.01 wt. % Neolone™ M-50 biocide (Rohm andHaas Company, Philadelphia, Pa., USA). The presence of corrosioninhibitor BTA inhibits the oxidation of metals on the wafer. The biocideis typically used in the concentrations prescribed by the supplier. Thepolishing fluids may also comprise small amounts of ammonium chloridefor polishing semiconductor substrates that contain copperinterconnects. The enumerated tests represent examples of the inventionand the alphabetically listed tests represent comparative examples.

Example 1 Imine Derivatives as Polishing Agents for CMP

The imine derivative compounds listed in Table 1 were used asnitrogen-containing polishing agents for CMP. The structures listedunder the headings “R¹” and “R²” correspond to the substituents instructure (I):

TABLE 1 (I)

Imine Derivative Compounds in Abrasive-Free Polishing Fluids Wt. TaNTEOS Cu Test Additive R¹ R² % Å/min Å/min Å/min 1 1,3-Diphenyl —NH—C₆H₅—NH—C₆H₅ 2 2385 −3 110 guanidine 2 Guanidine —NH₂ —NH₂ {•HCl} 2 1392 −197 hydrochloride 3 Tetramethyl- —N(CH₃)₂ —N(CH₃)₂ 2 1199 1 27 guanidine4 Formamidine —H —NH₂ 2 2197 −5 99 acetate {•CH₃COOH} 5 Acetamidine —CH₃—NH₂ {•HCl} 1 477 1 80 hydrochloride 6 Acetamidine —CH₃ —NH₂ {•HCl} 2450 3 81 hydrochloride A o-Methylisourea —OCH₃ —NH₂ 2 −8 −2 26 sulfate{•0.5 H₂SO₄} B 1-Methyl-3- —NH—CH₃ —NH—NO₂ 2 −18 0 51 nitroguanidine CArginine —NH₂ —NH—(CH₂)₃— 2 −18 −5 19 CH(NH₂)— C(═O)OH D Formamidine-—NH₂ —S(═O)OH 2 139 −1 75 sulfinic acid E Formamidine- —NH₂ —S(═O)OH 1−6 2 85 sulfinic acid  F* 2,2-Azobis —NH₂ —R²¹—N═N—R²²— 2 −1 −1 75(dimethyl- {•HCl} C(NH₂)═NH propionamidine)- {•HCl} di-HCl G (control) —— — −15 0 30 *R²¹ = —C(CH₃)₂—CH₂— R²² = —CH₂—C(CH₃)₂—

Imine derivative compounds, as described in Example 1 and Table 1,provided good TaN removal rates and good removal selectivities when thecompounds were free of electron-withdrawing substituents and containedat least one electron-donating substituent. Thus, the compounds of Tests1-6 contained an electron-donating substituent such as —NH₂; —NH—C₆H₅;or —N(CH₃)₂. These polishing agents provided abrasive-free TaN removalof at least 400 Å/min, with removal selectivities of at least 150relative to the dielectric (removal rate of TaN/removal rate of TEOS),and at least 5 relative to the metal (removal rate of TaN/removal rateof Cu). The preferred imine derivative compounds of Tests 1-4 containedonly substituents that were electron-donating or were hydrogen. Thesepolishing agents provided abrasive-free TaN removal of at least 1000Å/min, with removal selectivities of at least 1000 relative to thedielectric (Test 3), and at least 10 relative to the metal (Test 2). Incontrast, the compounds of Tests A-G contained at least anelectron-withdrawing substituent such as —OCH₃; —NH—NO₂; —SO₂H;—NH—(CH₂)₃—CH(NH₂)—C(═O)OH; or —C(CH₃)₂—CH₂—N═N—CH₂—C(CH₃)₂—C(NH₂)═NH.These polishing agents showed lower rates of TaN removal and poorremoval selectivities relative to the dielectric and the metal.

Example 2 Hydrazine Derivatives As Polishing Agents For CMP

The hydrazine derivative compounds listed in Table 2 were used asnitrogen-containing polishing agents for CMP. The results of thepolishing are given in Table 3. The structures listed under the headings“R³” through “R⁶” correspond to the substituents in structure (II):R³R⁴N—N R⁵R⁶  (II).

TABLE 2 Hydrazine Derivative Compounds in Abrasive-Free Polishing FluidsAdditive R³ R⁴ R⁵ R⁶ Carbohydrazide —H —H —H —C(═O—NH—NH₂ Acetichydrazide —H —H —H —C(═O)—CH₃ Semicarbazide —H —H —H —C(═O)—NH₂{•HCl}hydrochloride Formic hydrazide —H —H —H —C(═O)H 1,2-Diformyl- —H —C(═O)H—H —C(═O)H hydrazine Methylhydrazino- —H —CH₃ —H —C(═O)OH carboxylateOxalic —H —H —H —(C(═O))₂—NH—NH₂ dihydrazide Acetone azine — ═C(CH₃)₂ —═C(CH₃)₂

TABLE 3 Hydrazine Derivative Compounds in Abrasive-Free Polishing FluidsWt. TaN TEOS Cu Test Additive % Å/min Å/min Å/min 8 Carbohydrazide 21435 −2 74 9 Carbohydrazide 2 1059 −3 75 10 Carbohydrazide 2 1127 −4 10111 Carbohydrazide 2 1084 1 −35 12 Acetic hydrazide 2 1603 1.4 139 13Semicarbazide 2 1972 3.6 85 hydrochloride 14 Formic hydrazide 2 1484 2.1110 H 1,2-Diformylhydrazine 2 −2 −4 4 I Methylhydrazino- 2 −3 0 62carboxylate J Oxalic dihydrazide 2 −45 134 59 K Oxalic dihydrazide 0.94−14 0 107 L Oxalic dihydrazide 2 −15 −2 −9 M Acetone azine 2 10 −1 39

Hydrazine derivative compounds, as described in Example 2 and Tables2-3, provided good TaN removal rates and good removal selectivities whenthe compounds contained a hydrazine functionality (>N—NH₂) and no morethan one electron-withdrawing substituent. The hydrazine functionalitywas provided in these examples when R³ and R⁴ were both hydrogen. Thus,the compounds of Tests 8-14 contained a hydrazine functionality and nomore than one electron-withdrawing substituent. These polishing agentsprovided good TaN removal rates even though an electron-withdrawinggroup, such as a non-amide carbonyl group, was present. These polishingagents provided abrasive-free TaN removal of at least 1000 Å/min, withremoval selectivities of at least 500 relative to the dielectric (Test13), and at least 10 relative to the metal (Test 12). In contrast, thecompounds of Tests H-M either did not contain a hydrazine functionality(Tests H-I and M) or contained more than one electron-withdrawingsubstituent (i.e. two non-amide carbonyl groups; Tests J-L). Thesepolishing agents showed lower rates of TaN removal and poor removalselectivities relative to the dielectric and the metal.

According to the results of these Examples, as recited in Tables 1-3,high removal rates of the TaN barrier film are obtained with anabrasive-free polishing fluid that includes a nitrogen-containingpolishing agent. In particular, certain types of imine derivativecompounds and hydrazine derivative compounds provided good removal ratesfor TaN. The good removal rates for TaN, at least 400 angstroms perminute (Å/min), were observed for Tests 1-6 (Table 1) and Tests 7-14(Table 3). Preferred nitrogen-containing polishing agents provided TaNremoval rates of at least 1000 Å/min (Tests 1-4 and 7-14).

The results shown in Tables 1-3 provide data showing that adequateremoval of the barrier film (TaN) along with good removal selectivityversus the metal film (Cu) and the dielectric layer (TEOS) can occurwhen using abrasive-free polishing fluids containing nitrogen-containingpolishing agents. The CMP polishing fluid containing anitrogen-containing polishing agent that provides the advantages of highremoval rate, low erosion rates and low dishing rates as set forthabove. In particular, imine derivatives and hydrazine derivativecompounds accelerate the removal of tantalum-containing barriers. Inaddition, the fluid's reduced or abrasive-free particle contentdecreases dielectric erosion and dishing of interconnect metals.

1. A method for polishing tantalum-containing barrier materials of asemiconductor substrate with a polishing fluid including the step ofpolishing the semiconductor substrate with the polishing fluid polishingto remove at least a portion of the tantalum-containing barrier layer,the polishing fluid comprising: a nitrogen-containing compound having atleast two nitrogen atoms comprising at least one of a compound of aformula selected from the group comprising:

wherein R¹ comprises —H or —NH₂ and R², R³, R⁴, R⁵ and R⁶ independentlycomprise substituents selected from the group consisting of —H, ahydrocarbon group, an amino group, a carbonyl group, an imido group, anazo group, a cyano group, a thio group, a seleno group and —OR⁷ where R⁷comprises a hydrocarbon group, and the nitrogen-containing compoundbeing free of electron-withdrawing substituents; and the polishing fluidbeing capable of removing the tantalum-containing barrier materials froma surface of the semiconductor substrate without an abrasive.
 2. Themethod of claim 1, wherein the polishing fluid has 0 to 5 weight percentabrasive particles.
 3. The method of claim 1, wherein thenitrogen-containing compound contains the imine compound.
 4. The methodof claim 1, wherein the nitrogen-containing compound contains thehydrazine compound.
 5. A method for polishing tantalum-containingbarrier materials of a semiconductor substrate with a polishing fluidincluding the step of polishing the semiconductor substrate with thepolishing fluid polishing to remove at least a portion of thetantalum-containing barrier layer, the polishing fluid comprising: 0 to6 inhibitor for reducing the removal of an interconnect metal; 0 to 1weight percent abrasive particles; 0 to 25 oxidizing agent; 0 to 15complexing agent and 0.05 to 25 nitrogen-containing compound having atleast two nitrogen atoms comprising at least one of a compound of aformula selected from the group comprising:

wherein R¹ comprises —H or —NH₂ and R², R³, R⁴, R⁵ and R⁶ independentlycomprise substituents selected from the group consisting of —H, ahydrocarbon group, an amino group, a carbonyl group, an imido group, anazo group, a cyano group, a thio group, a seleno group and —OR⁷ where R⁷comprises a hydrocarbon group, and the nitrogen-containing compoundhaving an electron-donating substituent; and the polishing fluid beingcapable of removing the tantalum-containing barrier materials from asurface of the semiconductor substrate without an abrasive.
 6. Themethod of claim 5, wherein the polishing fluid contains no abrasiveparticles.
 7. The method of claim 5, wherein the nitrogen-containingcompound contains the imine compound and the imine compound contains atleast one selected from at least one of the group comprising1,3-diphenyl guanidine, guanidine hydrochloride, tetramethylguanidine,formamidine acetate and acetamidine hydrochloride.
 8. The method ofclaim 5, wherein the nitrogen-containing compound contains the hydrazinecompound and the hydrazine compound contains at least one selected fromat least one of the group comprising carbohydrazide, acetic hydrazide,semicarbazide hydrochloride, and formic hydrazide.
 9. The method ofclaim 5 wherein the tantalum-containing barrier layer contains tantalumand the polishing removes the at least a portion of the tantalum of thetantalum-containing barrier layer.
 10. The method of claim 5 wherein thetantalum-containing barrier layer contains tantalum-nitride and thepolishing removes the at least a portion of the tantalum-nitride of thetantalum-containing barrier layer.